SET-MATCH-FREE-DEFAULT

As described elsewhere (see free-variables), a rewrite, linear, or
forward-chaining rule may have free variables in its hypotheses, and
ACL2 can be directed either to try all bindings (``:all'') or just the
first (``:once'') when relieving that hypothesis, as a basis for
relieving subsequent hypotheses. This direction of :all or :once is
generally provided by specifying either :match-free :once or
:match-free :all in the :rule-classes of the rule. If neither
of these is specified, then the most recent set-match-free-default is
used by ACL2 to fill in this missing :match-free field.
See rule-classes. Except: If the last set-match-free-default specifies
nil, then ACL2 reverts to the behavior it had at start-up, as described
in Remarks (2) and (3) below.

Note: This is an event! It does not print the usual event summary
but nevertheless changes the ACL2 logical world and is so
recorded. It uses the acl2-defaults-table, and hence its effect is
local to the book or encapsulate form in which it occurs.

Remarks.

(1) The use of set-match-free-default has no effect on existing rules. In
order to change the behavior of existing rules with respect to free-variable
matching, see add-match-free-override.

(2) If you submit a rewrite, linear, or forward-chaining rule
with a free variable in a hypothesis, and no default setting was previously
specified with set-match-free-default or the default setting is nil,
and the rule is not within a book being processed with include-book,
certify-book, or rebuild, then a warning or error is caused. In
order to make this an error instead of a warning, see set-match-free-error.

(3) If you submit a rewrite, linear, or forward-chaining rule
with a free variable in a hypothesis, and no default setting has been
previously specified with set-match-free-default or the default setting
is nil, and no error is caused (see (2) above), then the default :all
is used.